The present invention relates to the decontamination of soil and the like (e.g. sediments, etc.) and, in particular, soils which are contaminated with metal as a result of the activities of human beings.
For the purposes of the present invention the following word(s) and expression(s), unless otherwise indicated, shall be understood as having the meaning indicated in respect thereto:
the word "soil" and the like (whether as noun, adjective, etc.) shall be understood as referring to unconsolidated mantle (whether natural or man made) including
material disposed on dry land masses; PA1 sediment including any bottom sediments of fresh or marine water systems; PA1 material which is wholly mineral or which in addition to mineral material, has an organic matter portion derived for example from plant or animal sources; organic material such as plant material would usually form part of the courser aggregate material as described hereinafter and would include, for example, tree stumps, ligneous particles, etc.; PA1 man-made mineral aggregate material and fill materials as well as man-made sediments arising in water-ways; and PA1 mineral residues from mining operations, such as those present in a tailings pond; PA1 the word "lixiviant" shall be understood as referring to a reagent capable of extracting a soluble constituent (i.e. solubilizing) from a solid mass (i.e. the lixiviation of a material); PA1 said coarse soil aggregate size fraction comprising components larger than the components of the second soil aggregate size fraction, said coarse soil aggregate size fraction having a metal concentration lower than that of the metal contaminated soil aggregate, said second soil aggregate fraction having a metal concentration higher than the metal concentration of said coarse soil aggregate size fraction, PA1 contacting said metal contaminated soil aggregate with an aqueous lixiviant for separating metal from said metal contaminated soil aggregate, said lixiviant comprising an organic acid component, said organic acid component comprising one or more carboxylic acids. PA1 contacting said contaminated soil aggregate with an aqueous lixiviant for separating metal, present in said contaminated soil aggregate, from said contaminated soil aggregate, said lixiviant comprising an organic acid component, said organic acid component comprising one or more carboxylic acids,
the word "aggregate" and any similar word (whether as noun, adjective, etc.) shall be understood as referring to or as characterizing (or emphasising) a "soil", "sediment", "material" or any portion thereof as a mass of individual particles or components of the same or varied size (e.g. the size of the components may be not uniform and may range from microscopic granules to 10 cm and larger); it is also to be understood that the particle size distribution of any particular soil mass, etc. may be different from that of another soil mass, etc.;
the words/expressions "contaminated", "metal contaminated" and the like, when used in relation to the words "soil", "sediment", "material" and the like, shall be understood as referring to that portion of the unconsolidated mantle (whether natural or man made) which is contaminated, in any way whatsoever, whether voluntarily or otherwise;
the words "decontaminate", "decontamination" and the like shall, in relation to metal contaminated material, be understood as referring to a process or the material produced by a process wherein the material or part thereof is provided which has a reduced level of metal as compared to the original material;
the words "classify", "classification" and the like shall, be understood as referring to the dividing of an aggregate material into size groupings or portions and as including separation of constituent components in accordance with size, separation of constituent components by magnetic separation, disaggregation to reduce particle size followed (as desired or necessary) by magnetic separation and/or separation by size (e.g. size separation by screening, gravity separation, etc.).
Metal contaminants include naturally occurring metals as well as metals which normally do not occur in nature (i.e. man made metals); the metals may be present as free or chemically combined species in any state of oxidation chemically possible. Metal contaminants include for example base metals, such as lead, zinc, mercury, cadmium, copper, nickel, chromium and cobalt, as well as other metals such as silver, molybdenum, selenium, arsenic and vanadium, etc. Metal contaminants also include radioactive metals (such as for example radioactive Co.sup.60 and plutonium) and other inorganic species (such as for example metal complexes based on arsenates, selenates, etc.) which when present in a soil (or sediment) are considered to be a contaminant.
The existence of aggregate material contaminated with metals can lead to serious environmental problems. Contaminated aggregate material if not properly contained or decontaminated can, for example, contribute to unsafe levels of metal(s) in surface and ground water as well as in the air (e.g. by contaminated dust). Aggregate material contaminated with metals can thus affect the health and well being of people living or working in the vicinity of or who come into direct contact with such material.
Contaminated soils, present, for example, on the sites of former or existing industrial complexes, pose a particularly serious problem relative to land use. Since such soils can pose a risk to the health of individuals, the presence of such soils can seriously affect the continued or alternate usage of such sites, e.g. redevelopment of a former industrial site for residential use may be precluded due to the presence of the contaminated soil.
The problems associated with contaminated soils are recognized by governments as being sufficiently important that some have taken steps to establish guidelines or limits for the amount of metal which may be present in soils. Thus, for example, the Waste Management Branch of the provincial government of the province of Ontario (Canada) has issued "Guidelines for the decommissioning and cleanup of sites in Ontario; February 1989". Representative guidelines are illustrated in the following tables wherein
Table a-1 shows the upper limits of normal concentrations of metals in soil for a number of metals; i.e. normal background levels of the listed metals; and
Table a-2 shows clean-up guidelines with respect to the levels of certain metals.
TABLE a-1 ______________________________________ Contaminant Guidelines Representing Upper Limits of Normal Concentrations in Ontario surface soil. Metal.sup.1 Urban Rural ______________________________________ Antimony 8 1 Arsenic 20 10 Cadmium 4 3 Chromium 50 50 Cobalt 25 25 Copper 100 60 Iron (%) 3.5 3.5 Lead 500 150 Magnesium -- 1 Manganese 700 700 Mercury 0.5 0.15 Molybdenum 3 2 Nickel 60 60 Selenium 2 2 Vanadium 70 70 Zinc 500 500 ______________________________________ Notes: .sup.1 All units are in ppm (.mu.g/g), dry weight, unless otherwise stated.
TABLE a-2 ______________________________________ CLEAN-UP GUlDELINES FOR SOIL Criteria for Proposed Land Use.sup.1 Agriculture/ Commercial/ Residential/Parkland Industrial Medium & Medium & Fine Course Fine Course Textured Textured Textured Textured Metal.sup.2 Soils Soils Soils Soils ______________________________________ pH 6-8 6-8 6-8 6-8 (recommended range) Arsenic 25 20 50 40 Cadmium 4 3 8 6 Chromium (VI) 10 8 10 8 Chromium (total) 1000 750 1000 750 Cobalt 50 40 100 80 Copper 200 150 300 225 Lead 500 375 1000 750 Mercury 1 0.8 2 1.5 Molybdenum 5 5 40 40 Nickel 200 150 200 150 Selenium 2 2 10 10 Silver 25 20 50 40 Zinc 800 600 800 600 ______________________________________ Notes: .sup.1 Clean-up guidelines recommended by the Phytotoxicology Section, Ai Resources Branch, Ministry of the Environment (Ontario). .sup.2 All units are in ppm (.mu.g/g), dry weight, unless otherwise stated.
No useful technology has been developed for effective removal of toxic heavy metals from soils (sediments, etc.). Procedures used to date have included in-situ containment or off-site disposal. Both procedures are expensive and in no way deal with detoxification of the soils (sediments, etc.).
A difficulty in dealing with contaminated soils (sediments, etc.) is the overall amount or mass of material which must be dealt with and the relatively small amounts of metals incorporated therein which are responsive for the unacceptable character of the soil.
Accordingly it would be advantageous to have means whereby metal contaminated soil aggregate may be treated to obtain a material which has a reduced level of metal as compared to the starting material.